# Benchmarking Orbital-Free Density-Potential Functional Theory of Electrified Metal-Solution Interfaces

## TL;DR

This paper benchmarks a new computational model for studying electrified metal-solution interfaces using orbital-free density-functional theory.

## Contribution

The study introduces a benchmark framework for evaluating DPFT models at interfaces and identifies optimal parameters for the TFvW functional.

## Key findings

- The TFvW kinetic energy functional outperforms the Pauli-Gaussian functional in modeling the electrical double layer.
- A smaller gradient coefficient in the TFvW functional improves accuracy for EDL modeling.
- The benchmark framework enables better assessment of orbital-free DFT models for electrochemical interfaces.

## Abstract

The electrical double layer (EDL) at the metal–solution
interface is a nanoscale region where quantum mechanical metal electrons
meet almost classical electrolyte species. Describing metal electrons
with orbital-free density-functional theory (DFT), the recently developed
density-potential functional theoretical (DPFT) model constitutes
a computationally efficient approach to modeling the EDL. However,
the performance of orbital-free DFT is less studied for interfaces
than for bulk phases. Herein, we develop a constant-potential Kohn–Sham–Poisson–Boltzmann
theory with exact kinetic energy as a benchmark for DPFT models. Solving
Kohn–Sham and Poisson–Boltzmann equations self-consistently,
we obtain electron density, electrostatic potential, and double-layer
capacitance of the EDL, which are then used to assess DPFT models
with Thomas–Fermi–von Weizsäcker (TFvW) or Pauli-Gaussian
kinetic energy functional. In general, TFvW outperforms the Pauli-Gaussian
kinetic energy functional for modeling EDL. In addition, a much smaller
gradient coefficient in the TFvW functional than the default value
of 5/3 is suggested for modeling the EDL. These findings are instrumental
to the future development of orbital-free DFT for electrochemical
interfaces.